This proposal targets the development of therapy against hemolytic uremic syndrome (HUS) caused by Shiga toxin (Stx)-producing E. coli (STEC). STEC strains are serious Category B pathogens associated primarily with food and waterborne acquired disease. They represent an important global emerging infection with relevance to foodborne illness and potential bioterrorism. The virulence of STEC is underscored by the very low infectious dose required to produce clinical disease. The treatment of STEC infection is complicated by potentially adverse consequences of routine administration of antibiotics. Diarrhea-associated (D+HUS) is a life-threatening complication of STEC infection, primarily the O157:H7 serotype, in children and the elderly that is heralded by the sudden onset of pallor and oliguria. It is associated with significant morbidity and, despite improvements in pediatric intensive care;the mortality rate from this disease remains 3-5%. There is no proven therapy for HUS that reduces mortality, the need for acute dialysis, or the occurrence of serious extra-renal events. The recent outbreaks, the spinach outbreak in particular, showed how vulnerable the population is to accidental contamination, and how urgently protective or therapeutic measure are needed. In this application we propose to use the newly developed oligonucleotide/aptamer technology which has gained foot as potential therapeutic agents in several systemic diseases in humans. In this application two teams have come together to achieve the goals of this application. They include a team with expertise in the design, synthesis and application of oligonucleotide/aptamer technology, and a team with expertise on STEC disease and the development screening and in vitro and in vivo evaluation of therapeutic agents against HUS. This proposal is designed to test the hypothesis that administration of specifically designed one or several aptamers against Stx2 and Stx1 will protect mice and piglets against the fatal systemic intoxication induced following systemic Stx challenge and oral E. coli O157challenge, respectively. The Specific Aim 1 focuses on the synthesis, selection, optimization and modification of aptamers. The Specific Aim 2 will apply in vitro assays to characterize and rank aptamers for in vivo studies. The Specific Aim 3 will evaluate the selected aptamers in the mouse toxicity model for efficacy and pharmacokinetics, and the Specific Aim 4 will perform preclinical evaluation in the well-established piglet model of oral E. coli O157:H7 infection.